INTRODUCTION

C HEMICALLY A CTIVATED B AEL S HELL

4.1 INTRODUCTION

Heavy metals as well as cationic dyes are extensively used by different kind of industries such as stainless steel, battery recycling plants, lead mining, electronic assembly, wood preservative, textile dyeing, fireworks, tanneries and metal plating industries. Among all the heavy metals and dyes, special attention has been given to Pb²⁺, Ni²⁺, Sr²⁺ ions and cationic dyes such as rhodamine B (RB) and methylene blue (MB) because of their common and extensive use in industries. Ingestion of Pb²⁺ and Ni²⁺ higher than its permissible level causes brain damage and dysfunction of the kidneys, liver and the central nervous system (Lalhruaitluanga and Jayaram, 2010;

Ngah and Fatinathan, 2010; Srivastava et al., 2006). On the contrary, Sr²⁺ has fatal effect if induced at high dosage as a result of its high solubility, long life and bio- toxicity (Ahmadpoura et al., 2010). Dyes create aesthetical and toxicological problems in the aqueous system. Therefore, the removal of these contaminants from wastewater is very important before its discharge. In this chapter, batch adsorption experiment results of single and multi component systems of selected metals and dyes are presented and discussed in detail using H2SO4 treated Bael shell adsorbent (SBS).

In preliminary performance evaluation test, SBS was found as an effective adsorbent for the removal of Pb²⁺, Ni²⁺, Sr²⁺ metal as well as cationic dyes (rhodamine B and methylene blue) from the targeted contaminants of this research work. The operating parameters that affect the adsorption process such as effect of pH, influence of other ions, multi component systems and solution temperature were monitored in this study to optimize the sorption process for its possible use as a low-cost adsorbent in the field of wastewater treatment to remove the single and multi contaminants from aqueous solution.

4.2 EXPERIMENTAL METHODS 4.2.1 Preparation of Synthetic Wastewater

Stock solutions of Pb²⁺, Ni²⁺, Sr²⁺, rhodamine B (RB) and methylene blue (MB) dye (1000 mg per litre of each metal solution separately) were prepared by dissolving appropriate quantity of Pb(NO3)2, NiCl2.6H2O, SrCl2.6H2O (Merck, India), RB and MB dye (C.I. 45170 and 52015, LOBA Chemie, India) in Millipore water, respectively. The chemical structure of RB and MB is illustrated in Appendix 1.

Equal mass of binary {(1000 mg of Pb²⁺ + 1000 mg of Ni²⁺) per litre, (1000 mg of

metal Pb²⁺ + 1000 mg of Sr²⁺) per litre and (1000 mg of Ni²⁺ + 1000 mg of Sr²⁺) per litre} and equal mass of ternary {(1000 mg of metal Pb²⁺ + 1000 mg of Ni²⁺ + 1000 mg of Sr²⁺) per litre} metal solutions were prepared for binary and ternary metal adsorption. Similarly, equal mass of each dye and each metal combination (150 mg of dye + 150 mg of metal) were prepared for another set of binary system. All stock solutions were shaken for 10 min at 180 rpm to obtain complete dissolution and then suitably diluted with Millipore water to get the required initial concentrations (100 to 300 mg/l for metals). Before mixing the adsorbent, the pH of the solution was adjusted using 0.1 N HCl or 0.1N NaOH. The pH of the solution was measured by pH meter (Eutech, model: 510).

4.2.2 Experimental Protocol

4.2.2.1 Adsorption Experiment

Adsorption experiments were carried out under batch mode at 30^oC, 40^oC and 50^oC.

Initially, the effect of acid treatment, solution pH, other ions and solution temperatures on sorption capacity of adsorbate (Pb²⁺, Ni²⁺, Sr²⁺, RB and MB dye) onto SBS were carried out only in single metal and dye system using fixed doses of adsorbents in 50 ml solution at 180 rpm. The pH of each solution was adjusted using required quantity of 1N HCl (or) 1N NaOH before mixing the adsorbent.

Subsequently, the effect of equal concentrations of binary and ternary system was conducted at natural pH using desired amount of adsorbent per 50 ml of multi-metal and (metal + dye) solutions. In a set of 250 ml Borosil conical flasks containing adsorbate solution (50 ml) of particular initial concentration was placed. Fixed doses of adsorbent were then added to the adsorbate solutions. The pH of the each solution was maintained at natural condition. Each sample was agitated in an incubating shaker (LabTech, Model LSI-1005R) at a particular temperature. Samples at different time intervals were withdrawn and the supernatant of metal and dye solution was separated by filtration using Whatman filter paper no. 42 and centrifuging dye at 5000 rpm, respectively. Final residual metal concentration was directly measured by flame atomic absorption spectrophotometer (AAS) (Varian spectra, AA240) with an air–

acetylene flame. The supernatant of RB and MB dye solutions were analyzed for the residual dye concentrations using UV–visible spectrophotometer (Perkin-Elmer, model: Lambdas 45) at the maximum wavelength (λ_max = 555 nm for RB and 667 nm

for MB) of the dyes. Calculation methods of adsorption capacity of adsorbent are given in Appendix 2.

4.2.2.2 Desorption Experiment

After adsorption, the elution of metals and dyes could be interesting for the reutilization of exhausted adsorbent and the recovery of the adsorbed metals and dyes.

The SBS utilized for the adsorption of initial Pb²⁺, Ni²⁺, Sr²⁺, RB and MB dye concentrations of 100 mg/l using 0.1 g of SBS in 50 ml at 30^oC were separated from solution by filtration. Then, metal and dye loaded adsorbents was mixed with 50 ml of different eluent solvents such as (0.1 M of HCl, HNO₃, CH₃COOH, NaOH; 0.01 M of EDTA; and hot distilled water) and agitated in incubating shaker (LabTech, Model LSI-1005R) at 30^oC temperature for 24 hr. After desorption, the supernatant of desorbed metal and dye eluent solutions were collected for the desorbed metal and dye analysis. The detailed procedure to calculate the amount of desorbed metal and dye is presented in the Appendix-2.

4.2.3 Adsorbent Characterization

(i) Scanning electron microscopy (SEM) (Leo, 1430 vp, Carl Zeiss, German) characterisation was carried out to observe the surface texture and porosity for two states of BS such as BS without activation and BS with H2SO4 activation (SBS). (ii) Due to the lower surface area of SBS adsorbent, to find out the BET surface area and monolayer volume of SBS, the single point surface area analyser (ChemiSorb 2720/2750) was used to analyze the nitrogen adsorption isotherm at -196^oC. Before measurement, the samples were degassed using Helium at 150^oC for 30 min. (iii) To resolve the functional groups and its wave numbers, spectra analysis was done for BS before and after adsorption using Fourier transform infrared spectrometer (FT-IR) (Perkin Elmer, PE-RXI) in the range of 500–4000 cm⁻¹. (iv) Zeta potential of SBS was measured using Beckman Coulter zeta potential analyzer (Delsa™ Nano C) at various pH based on the laser Doppler electrophoresis technique. (v) Energy dispersive X-ray spectroscopy (EDX) analysis was employed for further confirmation of metal adsorption over the surface of the SBS.